Iran on Tuesday warned Western countries that pressuring Tehran with sanctions while engaging in nuclear talks would jeopardise chances of reaching an agreement.

"This approach of pressure concurrent with negotiations will never work. These countries should not enter negotiations with such illusions and misinterpretations," foreign ministry spokesman Ramin Mehmanparast told a news conference.

"They have their own wrong conceptions and this will stop them from coming to a speedy and constructive agreement," he said in the conference broadcast by state network Press TV.

Western countries have stepped up sanctions on Iran over its nuclear program which Washington and its allies suspect is a cover for developing the capability to make an atomic bomb.

Tehran says it is only interested in using nuclear power for generating electricity and other peaceful projects.

Fresh U.S. legislation that targets Iran's oil industry is to come into force on June 28, days after the next meeting between Iran and world powers in Moscow.

European Union states are to impose a total ban on shipments of Iranian crude oil in July. European diplomats say this tactic will not change until Tehran takes tangible steps to curb its nuclear activity.

At the last talks between Iran and the powers, in Baghdad, Tehran pushed for the lifting of sanctions on its oil and banking sectors as a sign of goodwill.

But hours after the Baghdad talks concluded, U.S. Secretary of State Hillary Clinton said the dual-track approach of sanctions and negotiations would remain in place, saying there was "still a lot of work to do."

One of the Iranian negotiators' key demands in Baghdad was a clear statement from world powers of its right to engage all steps in the nuclear fuel cycle - from producing and preparing fuel to loading it and managing its disposal or reprocessing.

"Our rights for possessing the nuclear fuel cycle for peaceful purposes ... needs to be recognised and we will never do away with these rights," Mehmanparast told reporters.

Iran was looking forward to constructive talks in Moscow, he added, saying both sides needed to bring their viewpoints closer together to cooperate on all issues.

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